A genetic approach is proposed in order to study the biological functions and the physiological regulation of the cyclic AMP-dependent protein kinase enzymes. Inbred strains of mice will be screened for various characteristics of the protein kinase system, in hopes of finding a variant which could be subjected to genetic analysis. Additionally, developmental changes in the protein kinase system in lung and heart will be continued. Phosphoproteins whose degree of phosphorylatability change with proliferative and/or developmental state will be further characterized. The characteristics which will be screened for include: specific activities of both the protein kinase catalytic and cyclic AMP-binding activities and the isozymes of both the protein kinase holoenzyme and its dissociated subunits that can be resolved by DEAE-cellulose chromatography.